The invention relates to an apparatus for monitoring a machine part which moves or rotates about its own axis and moves with respect to a base.
In the field of vibration diagnosis it is customary to monitor inner components of epicyclic gears or components of a similar type with a sensor system which is arranged on fixed components. Acceleration pickups and solid-borne sensors are possible as sensors above all for this purpose.
In order to increase the operational reliability and ability to plan the maintenance and availability of the system, it has already been established practice for a relatively long time to subject said system to a noise analysis. This makes it possible to detect incipient damage, for example to transmission components or rolling bearings, in good time by virtue of the noise analysis and to correspondingly plan a repair.
DE 44 32 808 A1 discloses a sensor system for monitoring tools, such as, for example, monitoring drills, thread cutting tools, friction tools or milling tools. Vibration signals or solid-borne sound signals of machine elements which can move in a translatory or else rotational fashion and on which tools, workpieces or noise-generating component units are located are tapped in a wireless fashion at a housing which is stationary relative to the tool, and are passed onto a corresponding monitoring device or testing device. At the sensor end, the sensor system has just one housing body, one piezoelectric or electrodynamic vibration element and one primary coil. At the receiver end there is a secondary coil in a corresponding housing.
DE 103 25 801 A1 discloses a sound pickup which is used for the acoustic diagnosis of machines, for example for leakage detection in valves or for the diagnosis of bearings. The sound pickup comprises a piezoelectric measuring element and an electronic circuit which converts the measurement signal into a form which is suitable for transmission to an evaluation device. The sound pickup extracts the energy necessary to operate the electronic circuit from its surroundings. This auxiliary energy is generated from the sound signal which is to be picked up. The transmission of the output signal can take place via cable or alternatively in a wireless fashion by means of radio or infrared light. For example a piezoceramic which is provided with a seismic mass, and which is arranged in the sound pickup in addition to the piezoelectric measuring element, can be provided as a means for generating the auxiliary energy. In this variant, the auxiliary energy can be generated from the electrical measurement signal of the piezoelectric measuring element.
DE 199 24 955 A1 discloses an acoustic measuring instrument for measuring a transmission noise. The intention is to use this measuring instrument to acquire a measurement result which is adapted to the subjective hearing sensation and which can be used as an informative comparison variable. The measuring instrument comprises at least one sensor for sensing an air-borne sound signal and at least one sensor for sensing a solid-borne sound signal. The air-borne sound signal and the solid-borne sound signal and, if appropriate, measurement signals, such as a rotational speed signal, can easily be recorded by means of a two-channel DAT recorder. In this context, in a motor vehicle the solid-borne sound signal pickup is arranged directly on the transmission housing, a microphone is arranged as an air-borne sound signal pickup in the passenger compartment, and a tachometer for detecting the engine speed is arranged in the engine compartment. The sensors may be connected either in a wireless fashion or conductively to the DAT recorder.
DE 10 2006 058 689 A1 discloses a method and an apparatus for diagnosing the state of a machine component, in which the solid-borne sound of functional units is evaluated as vibration data in order to diagnose the state of machines or machine components. The recorded solid-borne sound signal is subjected to a known noise analysis for this purpose. The sensors are arranged on the housing of the machine which is to be monitored.
DE 10 2009 010 709 A1 discloses a movable wireless sensor and a method for the application thereof in a state and deployment monitoring system for a vehicle. A large number of wireless sensors are used in a vehicle, which sensors are configured to monitor one or more components of the vehicle and to transmit state data and/or deployment data to a data access point when these sensors are activated by a vibration of the vehicle. A movable wireless sensor, which may be temporarily located at a first position in order to monitor one or more components of the vehicle and which can then be moved to another position in order to monitor one or more other components of the vehicle, is arranged in the system. As a result, the total number of sensors used to monitor the vehicle is reduced.
DE 41 01 985 A1 discloses a method for determining irregularities of two elements which operate with one another. In particular damage to gearwheels and/or bearings on gearwheel transmissions are to be detected and their location determined by means of this method. An acceleration pickup is fitted to the gearwheel transmission to be examined. The solid-borne sound composite signal is converted into an electrical signal with the acceleration pickup. This signal is processed further and input into a computer. At the start of the measurement, moreover, the ratio of the frequency of the elementary signal of interest with respect to the input rotational frequency is set. The signals are then processed in the computer in accordance with the relationships for the solid-borne sound acceleration signal, and mean values are formed. The signal is evaluated by means of Fourier analysis.
In the case of sensors which are arranged on a transmission housing, an undefined transmission function of the sound propagation occurs because for structural reasons the vibrations which arise at the moving (for example pivoting) or rotating component are transmitted via a rolling contact (for example tooth engagement) which moves. In addition there is the continuously changing distance from the mounted sensor system, which distance in turn influences the transmission function of the signal to the sensor. In the case of a planetary gear mechanism there is also, for example, the further substantial disadvantage that the phase position of the planet gears adversely affects the measurement result of the vibration which ultimately occurs at the sensor. For this reason, in most cases an evaluation of the vibration signal with the objective of reliable diagnosis of individual components of such a system is extremely critical and unreliable.